Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on February 29, 2020, 11:39:27 pm

Title: Reverb tank.impedance question
Post by: Colas LeGrippa on February 29, 2020, 11:39:27 pm

I need a reverb tank for a.new build I m working on. The reverb will be external, driven by one of the OPT tap and amplified by a second amp.
There are a couple of different reverb tank input impedance out there,
from 8 to 1,200 ohm. Does the input impedance have to correspond to the input signal source
If so, I 'd have to get an 8 ohm. Would a 600 ohm do the job as well ?
Thanks

Title: Re: Reverb tank.impedance question
Post by: sluckey on March 01, 2020, 01:05:01 am

8Ω

Title: Re: Reverb tank.impedance question
Post by: glass54 on March 01, 2020, 01:19:07 am

Hi Colas,
I am attaching a document that may be of interest to you (and others) regarding Reverb tank parameters.
As a matter of interest the Hoffman AB763 project specifies a Rev Transformer p/n 022921 which is a 22k:8R transformer and a 4AB3C1B tank 8R in/2250R out.
You can check the rest from the attached doc.
Kind regards
Mirek

Title: Re: Reverb tank.impedance question
Post by: pdf64 on March 01, 2020, 04:27:01 am

Reverb tank drive coils are an inductive load, to get an even excitation level over the frequency range, need either current drive or, if voltage drive, increasing voltage with frequency.
See https://www.amplifiedparts.com/tech-articles/spring-reverb-tanks-explained-and-compared
If fed from a regular speaker output, from an 8 ohm input tank, a >40 dropper resistor should achieve that.

Title: Re: Reverb tank.impedance question
Post by: Colas LeGrippa on March 01, 2020, 07:58:51 pm

Thnx buddies

Title: Re: Reverb tank.impedance question
Post by: PRR on March 01, 2020, 08:21:46 pm

You want to be in the ballpark.

4 or 10 Ohms are all about the same.

600 Ohms is a different park, 2k yet another.

Title: Re: Reverb tank.impedance question
Post by: Colas LeGrippa on March 02, 2020, 10:39:23 am

Thank you Señor PRR, and what do you think about feeding it through a line out or a dropping resistor (8 ohm tap from OPT ) What value should have this resistor if connected to a 50W amplifier ? In other words what max ac voltage can the input transducer can handle ?


Colas

Title: Re: Reverb tank.impedance question
Post by: sluckey on March 02, 2020, 11:52:20 am

Take a look...

     https://el34world.com/charts/Schematics/files/Ampeg/Ampeg_echotwin.gif

EDIT... I should mention that this is a 4F type tank, ie, input impedance is 1475Ω. It is still driven from the main 8Ω speaker.

Title: Re: Reverb tank.impedance question
Post by: shooter on March 02, 2020, 12:21:39 pm

 :laugh:
you shoulda linked him to the original schematic  :icon_biggrin: